The present invention relates to the biomedical arts, particularly implantable electrodes. The present invention finds particular application in conjunction with cuff electrodes which are self-biased to curl around and snugly engage a nerve trunk, and will be described with particular reference thereto. It is to be appreciated, however, that the invention is also applicable to other types of implanted electrodes and biomedical devices.
Many types of nerve tissue damage do not heal. Such injuries leave a patient permanently without an appropriate nerve path for electrical signals or action potentials which travel from the brain to muscles or other biological tissue to cause a biological response. Similarly, such a discontinuity prevents action potentials from carrying sensory information or other biological feedback from the tissues to the brain. Moreover, there is also a tendency for action potentials to commence propagating naturally from below the injury site to the biological tissue causing an unconscious and unwanted biological response. Analogously, action potentials can propagate from above the injury site to the brain causing pain and erroneous sensory feedback.
Electrical potentials can be applied to nerve trunks and fibers to block the propagation of action potentials and for controllably initiating the propagation of action potentials in an upstream direction, a downstream direction, or both. Cuff electrodes, such as illustrated in U.S. Pat. No. 4,602,624 to Naples, Sweeney, and Mortimer controllably initiate and/or block action potentials in the nerves. Such cuff electrodes are self-biased to wrap around a nerve trunk in a spiral providing close contact. Because the electrode can be opened flat, it is surgically installed around the nerve fiber without cutting or damaging the nerve.
Although these prior art cuff electrodes have proven effective, they do have drawbacks. Primarily, the prior art cuff electrodes are labor intensive to manufacture. Metal foil strips are mounted and adhered to an elastomeric sheet. A second elastomeric sheet is stretched and laminated to the first elastomeric sheet. Apertures are provided in the second, stretched sheet to provide communication with the foil electrodes. Electrical leads are spot welded to the foil electrodes.
Interconnecting the leads with the electrodes at the cuff has drawbacks. First, the interconnection tends to increase the bulk of the electrode. Second, a failure of the spot weld requires removal of the electrode and the implantation of a new electrode.
Another drawback is that flat and annular sheet surface electrodes do not provide a uniform current density across their entire face. Rather, there tends to be a higher current flux adjacent the edges causing more rapid electrolytic degradation of the electrode edges. This concentration of the electrical flux at the edges accelerates edge degradation and corrosively reduces the size of the electrode. The size reduction, in turn, changes the electrical properties of the electrode.
The present invention provides a new and improved cuff electrode and method of manufacture which overcomes the above-referenced problems and others.